Speed of Sound in Air
Name:_____________________________
Partner(s):___________________________ Course: ________________ Time:_______
Purpose: Determine the speed of sound in air using different methods.
Introductory Video (Post-lab quiz my include questions from this video)
A. Temperature Method
Apparatus: PC with interface and temperature sensor.
Theory: Speed of sound in air (in m/s) at temperature T (in Kelvin) is given by;
v
kT
m
where γ = 1.40 (ratio of specific heats for air),
m = 4.8 x 10-26 kg (average molecular mass of air), and
k = 1.38 x 10-23 J/K (Boltzmann constant).
Procedure
Measure the room temperature using a temperature sensor, interface, and PC and
calculate the speed of sound.
a. Make sure that the power for the interface is turned on.
b. Plug in the temperature sensor to analog input A, white arrow on top.
c. Open PASCO Capstone software from the desktop.
d. Click Hardware Setup under Tools on the left, click on the interface input where the
sensor is connected and select Temperature Sensor. Click Hardware Setup again to
close it.
e. Double-Click Digits under Displays on the right, click Select Measurement, and select
Temperature.
f. Click Record.
DATA:
Room temperature, t = ___________0C = _________K.
Speed of sound (using temperature) = V = ____________
Q: Calculate the average molecular mass of air using the three most abundant gases found
in the Earth’s lower atmosphere, in the space below.
http://www.physicalgeography.net/fundamentals/7a.html
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B. Air-Column Resonance Method
Apparatus: Resonance tube apparatus, audio signal generator, speaker, stand w/clamp,
and water.
Theory: In wind instruments the wind (air) is made to resonate. Resonance makes the
sound audible. In this investigation a small speaker, connected to an audio signal
generator, will generate sound of required frequencies. The speaker is held above the
open end of the resonance tube, which has water. The water level can be changed by
lowering/raising the reservoir can.
As you lower the water level, keep your ear next to the speaker and listen carefully. At
the first resonance, L1 the sound will be louder. If you keep on lowering you will hear the
loud sound again at the second resonance, L2. The wavelength, λ is given by: λ = 2 (L2 L1). The speed of sound in air, V is given by: V = λ∙f, f = frequency.
DATA
Dial
Frequency
(Hz)
First
Resonance
Point, L1
Second
Resonance
Point, L2
Change in
Resonance
Points,
L2-L1
Wavelength,
λ
Speed of
sound, V
400
-
-
-
-
-
500
-
-
-
-
-
600
-
-
-
-
-
Average Speed of Sound
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C. Echo Method
Apparatus: Sound sensor, interface, PC, long cardboard tube, and meter stick.
Theory:
In this echo method, a sound pulse is made to travel along the tube, and the initial pulse
and the reflected pulse are detected with a sound sensor.
If the length of the tube is L, then the round trip distance of travel is 2L. If the travel time
is t, then the speed of sound, v is given by;
v
2L
.
t
Procedure:
1. Turn on the Pasco 850 interface, and connect the sound sensor to analog input A.
2. Open PASCO Capstone software from the desktop.
3. Click Hardware Setup under Tools on the left, click on the interface input where the
sensor is connected, and select Sound Sensor. Click Hardware Setup again to close it.
4. Click Recording Conditions, in the bottom-panel, and do the following.
a. Start Condition:
Condition type = Measurement Based
Data Source = Sound Intensity
Condition = Is above
Value = 1
b. Stop Condition:
Condition type = Time Based
Record time = 0.5s
c. Click, OK.
5. Double-Click Scope under Displays on the right, click Select Measurement on the
Y-axis, and choose Sound Intensity.
6. Place the cardboard tube on the laboratory table and hold the sound sensor close to the
open end.
7. Click Record, and snap your fingers at the open end of the tube as shown below.
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8. If the pulse is not captured, repeat procedure 7. If the pulse is visible, but not the echo,
drag the x-axis scale numbers until the pulse and echo are visible as shown below.
9. Click the Show Coordinates button (on top), right-click the coordinate, and select Tool
Properties, and change the significant figure to 4.
10. Use the Show Coordinates tool to find the time for initial pulse, time for echo, and
travel time and complete the data table below.
11. Repeat the measurements.
Length of
tube
(m)
Round trip
travel
Distance (m)
Time for
initial
pulse (s)
Time for
echo (s)
Round trip
Travel Time
(s)
Speed of
sound
(m/s)
12. Do the post-lab quiz (no password).
13. Turn in this hand-out (no conclusion today).
14. Do the course evaluations, for PHYS 201L.
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